[AIX] Use csect reference for function address constants

SUMMARY:
We currently emit a reference for function address constants as labels;
for example:

foo_ptr:
.long foo
however, there may be no such label in the case where the function is
undefined. Although the label exists when the function is defined, we
will (to be consistent) also use a csect reference in that case.

Reviewers: daltenty,hubert.reinterpretcast,jasonliu,Xiangling_L
Subscribers: cebowleratibm, wuzish, nemanjai

Differential Revision: https://reviews.llvm.org/D71144

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

@@ -177,6 +177,8 @@ class PPCAIXAsmPrinter : public PPCAsmPrinter {
 
   void SetupMachineFunction(MachineFunction &MF) override;
 
+  const MCExpr *lowerConstant(const Constant *CV) override;
+
   void EmitGlobalVariable(const GlobalVariable *GV) override;
 
   void EmitFunctionDescriptor() override;
@@ -1763,6 +1765,26 @@ void PPCAIXAsmPrinter::ValidateGV(const GlobalVariable *GV) {
     report_fatal_error("COMDAT not yet supported by AIX.");
 }
 
+const MCExpr *PPCAIXAsmPrinter::lowerConstant(const Constant *CV) {
+  if (const Function *F = dyn_cast<Function>(CV)) {
+    MCSymbolXCOFF *FSym = cast<MCSymbolXCOFF>(getSymbol(F));
+    if (!FSym->hasContainingCsect()) {
+      const XCOFF::StorageClass SC =
+          F->isDeclaration()
+              ? TargetLoweringObjectFileXCOFF::getStorageClassForGlobal(F)
+              : XCOFF::C_HIDEXT;
+      MCSectionXCOFF *Csect = OutStreamer->getContext().getXCOFFSection(
+          FSym->getName(), XCOFF::XMC_DS,
+          F->isDeclaration() ? XCOFF::XTY_ER : XCOFF::XTY_SD, SC,
+          SectionKind::getMetadata());
+      FSym->setContainingCsect(Csect);
+    }
+    return MCSymbolRefExpr::create(
+        FSym->getContainingCsect()->getQualNameSymbol(), OutContext);
+  }
+  return PPCAsmPrinter::lowerConstant(CV);
+}
+
 void PPCAIXAsmPrinter::EmitGlobalVariable(const GlobalVariable *GV) {
   ValidateGV(GV);
 

llvm/test/CodeGen/PowerPC/aix-reference-func-addr-const.ll

@@ -0,0 +1,32 @@
+; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mtriple powerpc-ibm-aix-xcoff < %s | FileCheck %s
+; RUN: llc -verify-machineinstrs -mcpu=pwr4 -mtriple powerpc64-ibm-aix-xcoff < %s | FileCheck --check-prefix=CHECK64 %s
+
+@foo_ptr = global void (...)* @foo
+declare void @foo(...)
+
+@bar_ptr1 = global void (...)* bitcast (void ()* @bar to void (...)*)
+define void @bar() {
+entry:
+  ret void
+}
+
+
+;CHECK:          .csect .data[RW]
+;CHECK-NEXT:     .globl  foo_ptr
+;CHECK-NEXT:     .align  2
+;CHECK-NEXT:     foo_ptr:
+;CHECK-NEXT:     .long   foo[DS]
+;CHECK-NEXT:     .globl  bar_ptr1
+;CHECK-NEXT:     .align  2
+;CHECK-NEXT:     bar_ptr1:
+;CHECK-NEXT:     .long   bar[DS]
+
+;CHECK64:         .csect .data[RW]
+;CHECK64-NEXT:         .globl  foo_ptr
+;CHECK64-NEXT:         .align  3
+;CHECK64-NEXT:    foo_ptr:
+;CHECK64-NEXT:         .llong  foo[DS]
+;CHECK64-NEXT:         .globl  bar_ptr1
+;CHECK64-NEXT:         .align  3
+;CHECK64-NEXT:    bar_ptr1:
+;CHECK64-NEXT:         .llong  bar[DS]